A stereomicroscope is conventionally used in microsurgical procedures on the eye. The so-called red-reflex illumination is utilized in the stereomicroscope in order to ensure a reliable and complete removal of the clouded eye lens in cataract surgery. Here, the ocular fundus diffusely reflects the incident illuminating light. The forward transparent sections of the eye appear in red transmitted light for the operating surgeon because of the absorption characteristics of the retina. Illuminating conditions of this kind are characterized in the following as "reflected transmitted light".
After drawing off the clouded eye lens with a so-called phaco-emulsificator, it is important for the operating surgeon to detect transparent lens residues, which may possibly still remain, in the forward eye section in order to likewise completely remove the same.
Up to now, efforts were made for the most part to intervene at the illuminating side in the stereomicroscope so that a red reflex resulted which was as homogeneous as possible in order to be able to clearly perceive lens residues in the forward section of the eye. In this connection, reference may be made to U.S. Pat. No. 5,126,877.
However, these interventions in the illuminating beam path of the particular stereomicroscope used did not always provide an adequate contrast of the substantially transparent media of the forward eye section.